Corrosion and Condition Assessment of Galvanized Steel Reinforcement in Concrete Structures Dr. Jane Jieying Zhang Critical Concrete Infrastructure October 4, 2012

Introduction and Outlines Corrosion of Galvanized Steel in Concrete –Projects Corrosion performance in chloride laden environments Comparison with carbon steel In HPC and OPC –Corrosion measurement techniques Half-cell potential techniques, Linear Polarization Resistance, AC impedance Autopsy of concrete Condition Assessment of Galvanized Steel in Concrete –A newly-started consortium project –Partners: MTQ, Corbec, Daam Galvanizing, Red River Galvanizing Inc, Galvcast MFG.Inc, Manitoba Infrastructure and Transportation (Manitoba DOT), South Atlantic LLC, New Jersey Galvanizing

Experimental 3

Corrosion Rate vs. Chloride Content Darwin et al. (2011) Cl th (gal) = 1.5 kg/m 3 Cl th (carbon) = 0.97 kg/m 3

Concretes with 1.5% and 3.0% of chlorides

Different Corrosion Stages of Galvanized Steel 6 Yeomans’ Model

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Galvanized Steel and Carbon Steel

High Chloride Concentration Galvanized Steel has clear advantage over carbon steel by its lower corrosion rate

Evidences 11

Evidences 12

Evidences 13

Condition Assessment Considerations of asset owners –Need a steel that is more corrosion resistant than carbon steel Knowledge has been established over years, especially corrosion initiation stage Corrosion rate of galvanized steel –In protection stage –In propagation stage. –Validation of corrosion mechanisms. –How to manage/maintain their asset afterwards Condition Assessment

Service life and Condition Assessment Condition assessment is the duty of infrastructure owners Safety Timely Maintenance Decision Making Repair Rehabilitation Removal

Four Governing Parameters for Initiation Stage T i  time to onset of corrosion C s  surface chloride concentration (Environmental Exposure) Cl th  chloride threshold value (Material Property, Steel) D  chloride diffusion coefficient (Material Property, Concrete) d c  depth of concrete cover over the reinforcing steel (Design Parameter)

Corrosion Initiation Stage 17 Galvanized steel provides longer corrosion initiation stage, because Cl th (galvanized steel)>Cl th (carbon Steel) Darwin et al. (2011)

The Governing Parameter for Propagation Stage 18 T i –c  time from onset of corrosion to surface crack I corr  corrosion rate (steel + concrete + environment) T i –c  accelerated corrosion environment in this study << in field condition T i –c  Comparative study with carbon steel

Half Cell Potential of Carbon Steel 19

20 Half Cell Potential Technique The most widely used corrosion assessment tool This guideline is for carbon steel only, but not for galvanized steel.

21 Condition Assessment Specifications of DOTs All based on ASTM C 876 or directly use ASTM C 876 The technique was pioneered by Stratfull and co-workers at the Caltrans, and now used worldwide. MTO “ Concrete Removal Survey a) Visual and Delamination Survey - A visual and delamination survey shall be carried out for all concrete removals. b ) Corrosion Potential Survey (Half-Cell) - When specified in the Contract Documents a corrosion potential survey will be carried out on all surfaces where concrete is to be removed based on corrosion potential criteria. Alberta Infrastructure uses V as the potential, which indicates corrosion, is occurring.

Half Cell Potential of Galvanized Steel 22

Using ASTM C 876 for Galvanized Steel Corrosion potentials of galvanized steel are different from those of carbon steel Half-cell potentials mean different corrosion risks for galvanized steel No guidelines for galvanized steel 23

From infrastructure owners MTO 2005 report “ The Long Term Performance of Three Ontario Bridges Constructed with Galvanized Reinforcement, ”By F. Pianca and H. Schell “According to ASTM C-876 if the steel reinforcement is passive the potential measured is small (0 to-200 mv) against a copper/copper sulphate cell. If the passive layer is failing and increasing amounts of steel are dissolving the potential moves towards –350mv. At more negative than -350mv the steel is usually corroding actively. The interpretation of the active/passive steel reinforcement in concrete is based on empirical observation of the probability of corrosion in structures containing black steel. However a means of interpreting half-cell data is not currently available in the literature for galvanized reinforcement in concrete. ” 24

Zinc used for effective corrosion control of steel reinforcement 25 The lower the electrode potential, the higher the tendency for the metal to corrode Zinc, for example, has a tendency to corrode when connected to steel. 1.The corrosion potential difference (up to 400 mV) of Zinc and Iron is the reason for use of Zinc for protection of steel. 2.Zinc’s lower potential ( beneficial fact) not recognized in the condition assessment guidelines for carbon steel

From Field Inspection A 2002 Report to ILZRO and AHDGA Use condition assessment guideline for black steel (ASTM C-876 ) 26

27 NRC’s Corrosion Assessment Techniques for Concrete Half-Cell Potential Method – tendency and probability Linear Polarization Resistance Method –R p AC Impedance Method Electrochemical Impedance Spectrum –R e, C d, R p

NRC Research Expertise in Corrosion Corrosion of Reinforcing Steel in Concrete Corrosion Mechanisms Performance of Carbon Steel and Corrosion Resistant Steels Galvanic Coupling Corrosion Corrosion in Concrete Patch Repair Service Life Prediction and Performance-based Durability Design Condition Assessment of Corrosion Condition Assessment of Galvanized Steel in Concrete Structures 28

Laboratory Experimental Study 29

Field Experimental Study 30

Current Data on carbon steel and galvanized steel 31 According to ASTM guidelines for carbon steel, all galvanized steel bars, measured below -400 mV, are corroding fast. The actual corrosion condition of galvanized steel: passivation (no corrosion)

Challenges for Galvanized Steel from using Carbon Steel Guidelines For a surveyed potential falling between -350 mV to about -550 mV vs. CSE, a typical range indicating that carbon steel has started to corrode fast, does it mean that –zinc coating is passivated (not corroding)? OR –substrate carbon steel has started to corrode fast? 32

Research Project Condition assessment and corrosion mitigation of galvanized steel in concrete bridge decks, for –Better service life prediction – Timely maintenance strategy –Extension of service life –Experimental Investigation Characterize corrosion of galvanized steel Identification of Key parameters: chloride concentrations, concrete mix design, and environmental exposures –Modeling and Develop guidelines for interpretation of corrosion measurement –Field Validation

Preliminary Data from Electrochemical Cell Study 34 ASTM C ASTM C ######

Partners of the newly started consortium project MTQ (Quebec DOT) Corbec Daam Galvanizing Red River Galvanizing Inc. Galvcast MFG.Inc Manitoba Infrastructure and Transportation (Manitoba DOT) South Atlantic LLC New Jersey Galvanizing Need more support of the consortium in order to conduct field studies for validation Contact : Our business manager

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